1. Field of the Invention
The invention relates to a process for heat integration in engineering processes in which, in a heat carrier circuit, a heat carrier medium takes up heat from a first process stream in a first heat exchanger and releases it to a refrigeration system, and in addition a second process stream is cooled using the refrigeration system.
2. Description of the Related Art
Against the background of increasing demands with respect to energy efficiency and cost efficiency, heat integration is increasingly gaining importance in engineering processes. Different variants of heat integration are known in the specialist area and some have established themselves in large scale industrial plants. Customarily, in this case, temperature differences between process streams are exploited, for example when a hot stream from a reactor is used in order to heat up the cooler feed to the reactor. In cases where the temperature difference between the streams is too small in order to implement a direct heat exchange, frequently refrigeration systems or heat pumps are used in order to make the heat usable at the corresponding temperature levels. In addition to steam jet or compression refrigeration systems, here, in particular, absorption refrigeration systems or absorption heat pumps may be mentioned.
In an absorption refrigeration machine the absorption capacity of a selected material pair comprising a refrigerant and an absorbent is utilized (see, e.g. “Dubbel Taschenbuch für den Maschinenbau” [Dubbel's handbook of mechanical engineering], 21st edition, Verlag Springer, Berlin, 2005, section M 1.4.3). In this machine the refrigerant vaporizes at low pressure in an evaporator and thereby removes heat from a process stream at a low temperature level. The resultant refrigerant vapor is absorbed by the absorbent with removal of heat in an absorber. The refrigerant-enriched absorbent is pumped to a higher pressure level into an expeller in which, with supply of heat from a process stream at a higher temperature level, the refrigerant is expelled again. The depleted absorbent is recirculated back to the absorber. The refrigerant vapor is liquefied at the higher pressure level in a condenser using cooling water and fed back to the evaporator. In the industrial sector, in particular for applications at low temperatures, the material pair ammonia as refrigerant and water as absorbent has proven itself. In addition, the material pair water as refrigerant and lithium bromide as absorbent has become established.
U.S. Pat. No. 4,530,826 describes a possibility of using waste heat in an engineering process, which waste heat is available at a relatively low temperature level. In this case product streams from distillation, absorption or desorption columns and also from reactors are used, in order to remove or supply heat from or to other streams at different locations of the respective engineering process by means of an absorption refrigeration system or an absorption heat pump. The principle is illustrated by way of example by processes for producing acrylonitrile, methacrylic acid, acrylic acid, prussic acid and formaldehyde.
In the PCT application WO 2008/034798 A1, a process is described for generating refrigeration energy in a polycondensation process in which wastewater vapor formed as a byproduct is converted by condensation into wastewater. The heat energy liberated during condensation of the wastewater vapor is taken up by a heat carrier medium and fed to a refrigeration generator having a thermal compressor and converted into refrigeration energy. The refrigeration energy can be used for cooling a process medium or else for conditioning air in an air conditioning appliance.
Although refrigeration systems and heat pumps are already used in numerous engineering systems for heat integration, there is still a requirement for improving the technology, especially with respect to even broader usability.